It does indeed work fine with people I call or receive calls from who use cell phones, and other types of lines, but the Ooma line that I call frequently is the one that is oddly not working right. I suspected that it could be an Ooma thing, but the odd part was the prior to an upgrade to a new OBi firmware, I had no issues calling that Ooma number. Hence my thinking that it could be related to something on the OBi.